Size-fractionated phytoplankton standing stock and primary production in the Bohai Sea during late spring

During June 1997 cruise by R/V Science No.l, observations on temporal and spatialvariations of the size-fractionated phytoplankton standing stock and primary production were carried out in the Bohai Sea. The size-fractionated chlorophyll a (Chl a) and primary production, photosynthet-ically available radiation (PAR), as well as the related physico-oceanographic and zooplanktonic parameters were measured at five time-series observation stations representing sub-areas of the sea. Results obtained show that there were the marked features of spatial zonation of Chl a and primary production in the Bohai Sea. The values in the Laizhou Bay, the Liaodong Gulf and the Bohai Gulf were high and showed close relation with tidal fluctuations, i.e. high Chl a concentration occurred during high tide in the Laizhou Bay, and during low tide in the Liaodong Gulf and the Bohai Gulf. In the strait and the central region of the Bohai Sea, the values were relatively low and no relationship with tidal fluctuation could be foun

Size-fractionated phytoplankton standing stock and primary production in the Bohai Sea during late spring

--During June 1997 cruise by R/V Science No. 1, observations on temporal and spatial variations of the size-fractionated phytoplankton standing stock and primary production were carried out in the Bohai Sea. The size-fractionated chlorophyll a (Chl a) and primary production, photosynthetically available radiation (PAR), as well as the related physico-oceanographic and zooplanktonic parameters were measured at five time-series observation stations representing sub-areas of the sea. Results obtained show that there were the marked features of spatial zonation of Chl a and primary production in the Bohai Sea. The values in the Laizhou Bay, the Liaodong G ulf and the Bohai Gulf were high and showed close relation with tidal fluctuations, i.e. high Chl a concentration occurred during high tide in the Laizhou Bay, and during low tide in the Liaodong Gulf and the Bohai Gulf. In the strait and the central region of the Bohai Sea, the values were relatively low and no relationship with tidal fluctuation could be found. Chlorophyll a concentration vertically decreased from surface to bottom in the Liaodong Gulf and the Bohai Gulf, while it increased in the Laizhou Bay, the strait and the central region of the Bohai Sea, and the highest value was encountered at the bottom. Size-fractionation results showed that nano - combining pico -plankton ( ＜ 20 μm) predominated in phytoplankton communities of the Bohai Sea during late spring. The average contribution to total Chi a in each station ranged 76% ～ 95% (mean is 87% ). The contribution of net ( ＞ 20μm), nano - (2～ 20μm) and picoplankton ( ＜ 2 μm) was 13%, 63% and 24% to total production, and 9%, 53% and 38% to total Chl a, respectively. It proved the importance of nano - and pico -plankton in phytoplankton communities in the Bohai Sea ecosystems. In this paper the factors, such as light intensity and zooplankton grazing pressure, governing standing stock and production of phytoplankton in the Bohai Sea were also discussed.